Tree 41: Tree of Heaven
First introduced from China in 1751, this tree is named due to its very rapid growth which suggests it could reach the heavens! It can attain a height of 25 metres. Its attractive leaves, flowers and fruits have caused it to become a favourite specimen in many parks, formal gardens and public spaces.
The bark of the tree is pale grey, with a vertical snake-like pattern. It has large, pinnately compound leaves, with up to 21 leaflets, giving an appearance similar to that of Ash. These unfold red in May or June and there is a single tooth at the base of each leaflet. If crushed, they release a characteristic bad odour! Small, yellow-green dioecious flowers are formed in panicles at the ends of branches, in July, and these are effective at attracting pollinators. Red-tinged, winged fruits are formed in the autumn which hang like ‘keys’ from female trees- in urban areas, most trees are female.
Chinese medicine makes use of the dried bark from the trunk and root for treatment of ailments such as diarrhoea, baldness and epilepsy- though a poor evidence base has prevented use in mainstream Western medicine. A yellow dye can be extracted from the leaves and the leaves and bark naturally produce an insect repellent.
The Tree of Heaven can produce 100’s of seedlings and will produce suckers very rapidly if cut-back, thereby forming a dense thicket. The suckers are strong and vigorous, sometimes seen pushing up through tarmac or disturbing the foundations of buildings. It shows allelopathy i.e. it makes and sends chemicals into the ground which inhibit the germination and growth of other species. These traits mean that it is regarded as an invasive species, is not always welcome and is covered by regulation. ‘Tree of Hell’ is a name that some have given it! The following passage from Betty Smith’s 1943 novel A Tree Grows in Brooklyn sums up the situation:
“There’s a tree that grows in Brooklyn. Some people call it the Tree of Heaven. No matter where its seed falls, it makes a tree which struggles to reach the sky. It grows in boarded-up lots and out of neglected rubbish heaps. It grows up out of cellar gratings. It is the only tree that grows out of cement. It grows lushly . . . survives without sun, water, and seemingly without earth. It would be considered beautiful except that there are too many of it.”